Year comes from PIE *yer-o- (“year”, “season”), which is probably related to the verbal root *ei- meaning “to make” as in “to make/complete a full cycle”.
Month stems from Proto-Germanic *menoth- related to *menon- “moon”.
Week is derived from Proto-Germanic *wikon “turning” or “succession” as describing the change of lunar phases. The Germanic peoples adopted this convention from the Romans; there is no record of earlier tracking of weeks from them.
Day comes from from PIE *dhegh “to burn”. Funnily, it is not related to Latin dies, which comes from PIE root *dyeu- “to shine”. Just a happy coincidence.
Hour came from Latin hora “hour, season”, from Greek hora “limited period”, from PIE *yer-o- “season”… just like year did!
Minute comes from the Latin minuta meaning a small part. It was actually used originally as minuta prima as the first 1/60 division of a circle (then an hour)…
… the second division was called secunda minuta, and that’s where we got second from!
Originally published in The blind mouse.